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Robin K. Dutta - One of the best experts on this subject based on the ideXlab platform.

  • Partition Equilibrium of phenol red in aqueous polymer surfactant system determination of critical aggregation concentration
    Journal of Molecular Liquids, 2010
    Co-Authors: Bornali Boruah, Biren Gohain, Palash M. Saikia, Robin K. Dutta
    Abstract:

    Abstract Acid–base Equilibrium of phenol red (PR), a sulphonephthalein dye, was studied spectrophotometrically in aqueous media containing water soluble nonionic polymers viz., polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A Partition Equilibrium method was utilized to determine the Equilibrium constant of Partition of the PR between micellar pseudo phase and aqueous phase and the critical aggregation concentration (CAC) of SDS in buffered aqueous systems containing the neutral polymers. The pH dependent association constants, Kass of PR with SDS–PVA, and SDS–PEG system increase in the order PEG 200

  • Partition Equilibrium of phenol red in aqueous polymer–surfactant system: Determination of critical aggregation concentration
    Journal of Molecular Liquids, 2010
    Co-Authors: Bornali Boruah, Biren Gohain, Palash M. Saikia, Robin K. Dutta
    Abstract:

    Abstract Acid–base Equilibrium of phenol red (PR), a sulphonephthalein dye, was studied spectrophotometrically in aqueous media containing water soluble nonionic polymers viz., polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A Partition Equilibrium method was utilized to determine the Equilibrium constant of Partition of the PR between micellar pseudo phase and aqueous phase and the critical aggregation concentration (CAC) of SDS in buffered aqueous systems containing the neutral polymers. The pH dependent association constants, Kass of PR with SDS–PVA, and SDS–PEG system increase in the order PEG 200

  • A Partition Equilibrium Study of Sulfonephthalein Dyes in Nonionic Surfactant Systems at High pH
    Journal of Surface Science and Technology, 2007
    Co-Authors: Palash M. Saikia, Robin K. Dutta
    Abstract:

    The acid base equilibria of two sulfonephthalein dyes, viz., bromothymol blue (BTB) and bromocresol green (BCG) in aqueous nonionic micellar solutions of Triton X100, Tween 20, Tween 40, Tween 60 and Tween 80 have been investigated spectroscopically using a Partition Equilibrium method. A red shift in the λ max of the visible absorption band corresponding to the base forms of the dyes with increase in surfactant concentration was observed at and above pH 9.0. For a particular dye-surfactant system the red shift increases with the increase in pH and was found to be greater for TX 100 than for the Tween surfactants. Red shift of the λ max of BTB was observed to be greater than that of BCG in all of the nonionic micellar systems investigated in buffered medium. The observed red shift has been attributed to stabilization of the base form of the dye by the polyoxyethylene (POE) head groups. The stabilization effect was found to decrease with increase in the number of carbon atom and unsaturation in the hydrophobic tail of the surfactant molecules. The Equilibrium constant of the Partition of the dyes between micellar and aqueous pseudophases (K ass ) was found to be greater for the more hydrophobic BTB than the less hydrophobic BCG. With the surfactants the K ass increases in the order Tween 80 < Tween 60 < Tween 40 < Tween 20 < TX 100. The pK a2 of the dyes were predicted using a Partition Equilibrium model and found to be in good agreement with the experimental values.

  • effects of alcohol on Partition Equilibrium of phenol red in micellar solutions and o w microemulsions of anionic surfactants
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005
    Co-Authors: Surashree Sarma, Munindra Bora, Robin K. Dutta
    Abstract:

    Abstract The effects of alcohol, viz., propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, pentan-1-ol, pentan-2-ol and pentan-3-ol on Partition Equilibrium of phenol red (PR) in anionic micelles and in o/w microemulsions of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) with buffered aqueous pseudophase. The results have been correlated with incorporation of the alcohol to different regions in the micelles and oil–water interface and enhanced incorporation of the dye to the oil–water interface with decreasing droplet curvature. Preferred incorporation of alcohol in the interfacial headgroup region lowers the Partition Equilibrium constant, K p initially up to an alcohol to surfactant w/w ratio of 1:1 in both micellar solutions and o/w microemulsions. The K p increases as the ratio exceeds 1:1 due to increased solubilization of the alcohol towards the hydrocarbon chain region of the surfactants rather than in the headgroup region. In the microemulsion systems, the K p increases with increase in oil volume fraction due to enhanced incorporation of the dye in the palisade layer of the oil–water interface with decreased droplet interface curvature. At a given volume fraction of oil, the Partition Equilibrium constant increases on changing the alcohol in the order: propan-2-ol

  • Partition of bromophenol blue in toluene/water/sodium bis(2-ethylhexyl)-sulfosuccinate water-in-oil microemulsions
    Journal of Surfactants and Detergents, 2005
    Co-Authors: Surashree Sarma, Robin K. Dutta
    Abstract:

    The Partition of bromophenol blue between oil-water interfaces and water droplets in water-in-oil microemulsions of toluene/water/sodium bis(2-ethylhexyl)sulfosuccinate was studied by a spectroscopic method at different water fractions and pH. The Partition Equilibrium constant, Kp, between the two domains decreased considerably with an increase in the water fraction and pH. The decrease in Kp with an increase in the water fraction suggests the retention of more dye molecules in water. The decrease in Kp with an increase in pH has been attributed to a lower tendency of the base form to associate with the anionic oil-water interface compared with that of the acid form and to an increase in the negative charge density at the oil-water interface at a higher pH.

Takashi Kakiuchi - One of the best experts on this subject based on the ideXlab platform.

  • a theory of voltammetry of ion transfer across a liquid membrane in the absence of supporting electrolytes using the nernst planck equation and electroneutrality assumption
    Electrochimica Acta, 1998
    Co-Authors: Takashi Kakiuchi
    Abstract:

    A theory of cyclic voltammetry of ion transfer across a liquid membrane has been presented based on the Nernst–Planck equation and the electroneutrality assumption. The initial conditions are given by the Partition Equilibrium of ions between the membrane and the two bathing solutions. Current–potential curves are calculated for the case of reversible transfer of Na+ across the membrane/solution boundary and the complete dissociation of electrolytes in the membrane, taking account of time-dependent solution resistance and the diffusion potential. The peaks appear only in the limited range of the scan rate at a given thickness of the membrane. The model explains wide peak separation which has been reported in the voltammetry of ion transfer in the presence of lipophilic ions. Upon imposing the voltage across the membrane, the phase-boundary potential at each side of the membrane varies with time and, hence, the ion Partitioning at the membrane/bathing solution interface is a time-dependent process.

  • A theory of voltammetry of ion transfer across a liquid membrane in the absence of supporting electrolytes using the Nernst–Planck equation and electroneutrality assumption
    Electrochimica Acta, 1998
    Co-Authors: Takashi Kakiuchi
    Abstract:

    A theory of cyclic voltammetry of ion transfer across a liquid membrane has been presented based on the Nernst–Planck equation and the electroneutrality assumption. The initial conditions are given by the Partition Equilibrium of ions between the membrane and the two bathing solutions. Current–potential curves are calculated for the case of reversible transfer of Na+ across the membrane/solution boundary and the complete dissociation of electrolytes in the membrane, taking account of time-dependent solution resistance and the diffusion potential. The peaks appear only in the limited range of the scan rate at a given thickness of the membrane. The model explains wide peak separation which has been reported in the voltammetry of ion transfer in the presence of lipophilic ions. Upon imposing the voltage across the membrane, the phase-boundary potential at each side of the membrane varies with time and, hence, the ion Partitioning at the membrane/bathing solution interface is a time-dependent process.

Surashree Sarma - One of the best experts on this subject based on the ideXlab platform.

  • effects of alcohol on Partition Equilibrium of phenol red in micellar solutions and o w microemulsions of anionic surfactants
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005
    Co-Authors: Surashree Sarma, Munindra Bora, Robin K. Dutta
    Abstract:

    Abstract The effects of alcohol, viz., propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, pentan-1-ol, pentan-2-ol and pentan-3-ol on Partition Equilibrium of phenol red (PR) in anionic micelles and in o/w microemulsions of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) with buffered aqueous pseudophase. The results have been correlated with incorporation of the alcohol to different regions in the micelles and oil–water interface and enhanced incorporation of the dye to the oil–water interface with decreasing droplet curvature. Preferred incorporation of alcohol in the interfacial headgroup region lowers the Partition Equilibrium constant, K p initially up to an alcohol to surfactant w/w ratio of 1:1 in both micellar solutions and o/w microemulsions. The K p increases as the ratio exceeds 1:1 due to increased solubilization of the alcohol towards the hydrocarbon chain region of the surfactants rather than in the headgroup region. In the microemulsion systems, the K p increases with increase in oil volume fraction due to enhanced incorporation of the dye in the palisade layer of the oil–water interface with decreased droplet interface curvature. At a given volume fraction of oil, the Partition Equilibrium constant increases on changing the alcohol in the order: propan-2-ol

  • Partition of bromophenol blue in toluene/water/sodium bis(2-ethylhexyl)-sulfosuccinate water-in-oil microemulsions
    Journal of Surfactants and Detergents, 2005
    Co-Authors: Surashree Sarma, Robin K. Dutta
    Abstract:

    The Partition of bromophenol blue between oil-water interfaces and water droplets in water-in-oil microemulsions of toluene/water/sodium bis(2-ethylhexyl)sulfosuccinate was studied by a spectroscopic method at different water fractions and pH. The Partition Equilibrium constant, Kp, between the two domains decreased considerably with an increase in the water fraction and pH. The decrease in Kp with an increase in the water fraction suggests the retention of more dye molecules in water. The decrease in Kp with an increase in pH has been attributed to a lower tendency of the base form to associate with the anionic oil-water interface compared with that of the acid form and to an increase in the negative charge density at the oil-water interface at a higher pH.

  • A Partition Equilibrium study of sulfonephthalein dyes in anionic surfactant systems: determination of CMC in buffered medium
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
    Co-Authors: Palash M. Saikia, Surashree Sarma, Biren Gohain, Achyut Kalita, Robin K. Dutta
    Abstract:

    Abstract A spectrophotometric method has been reported which can be used to simultaneously determine Partition Equilibrium constant of anionic sulfonephthalein (acid–base indicator) dyes between micellar pseudophase and aqueous phase, and critical micelle concentration (CMC) of the surfactants in buffered aqueous anionic surfactant systems. The method is based on two assumptions: (1) only one form of the dye goes into the micellar pseudophase, which holds for similarly charged dye–surfactant systems and (2) the activity terms for the conjugate acid and base forms of the dye can be combined in buffered solution. An absorption band, which decreases with addition of surfactant, is used for the analysis. The method has been found suitable to the systems of sulphonephthalein (anionic) dyes, viz. bromophenol blue (BPB), bromothymol blue (BTB) and thymol blue (TB) with anionic surfactants, viz. sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfonate (SDSN). The Partition Equilibrium constants have been found to be dependent on hydrophobicity of the dye and pH of the solutions. The CMC's have been found to increase with increase in pH for a particular buffer system. The method can conveniently be used for study of interactions in such dye–surfactant systems and to determine CMC of the anionic surfactants in buffered solutions.

  • A Partition Equilibrium Study of Benzene/Water/Sds-Butanol Oil/Water Microemulsions
    Journal of Chemical Research, 2003
    Co-Authors: Surashree Sarma, Biren Gohain, Robin K. Dutta
    Abstract:

    Partition of a sulfonephthalein dye, viz., phenol red, between the pseudophases in oil/water benzene/water/SDS-butanol microemulsions has been studied by UV-VIS spectroscopy and the Partition Equilibrium constants have been correlated with the microstructure of microemulsions and effect of cosurfactant.

Palash M. Saikia - One of the best experts on this subject based on the ideXlab platform.

  • Partition Equilibrium of phenol red in aqueous polymer surfactant system determination of critical aggregation concentration
    Journal of Molecular Liquids, 2010
    Co-Authors: Bornali Boruah, Biren Gohain, Palash M. Saikia, Robin K. Dutta
    Abstract:

    Abstract Acid–base Equilibrium of phenol red (PR), a sulphonephthalein dye, was studied spectrophotometrically in aqueous media containing water soluble nonionic polymers viz., polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A Partition Equilibrium method was utilized to determine the Equilibrium constant of Partition of the PR between micellar pseudo phase and aqueous phase and the critical aggregation concentration (CAC) of SDS in buffered aqueous systems containing the neutral polymers. The pH dependent association constants, Kass of PR with SDS–PVA, and SDS–PEG system increase in the order PEG 200

  • Partition Equilibrium of phenol red in aqueous polymer–surfactant system: Determination of critical aggregation concentration
    Journal of Molecular Liquids, 2010
    Co-Authors: Bornali Boruah, Biren Gohain, Palash M. Saikia, Robin K. Dutta
    Abstract:

    Abstract Acid–base Equilibrium of phenol red (PR), a sulphonephthalein dye, was studied spectrophotometrically in aqueous media containing water soluble nonionic polymers viz., polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A Partition Equilibrium method was utilized to determine the Equilibrium constant of Partition of the PR between micellar pseudo phase and aqueous phase and the critical aggregation concentration (CAC) of SDS in buffered aqueous systems containing the neutral polymers. The pH dependent association constants, Kass of PR with SDS–PVA, and SDS–PEG system increase in the order PEG 200

  • A Partition Equilibrium Study of Sulfonephthalein Dyes in Nonionic Surfactant Systems at High pH
    Journal of Surface Science and Technology, 2007
    Co-Authors: Palash M. Saikia, Robin K. Dutta
    Abstract:

    The acid base equilibria of two sulfonephthalein dyes, viz., bromothymol blue (BTB) and bromocresol green (BCG) in aqueous nonionic micellar solutions of Triton X100, Tween 20, Tween 40, Tween 60 and Tween 80 have been investigated spectroscopically using a Partition Equilibrium method. A red shift in the λ max of the visible absorption band corresponding to the base forms of the dyes with increase in surfactant concentration was observed at and above pH 9.0. For a particular dye-surfactant system the red shift increases with the increase in pH and was found to be greater for TX 100 than for the Tween surfactants. Red shift of the λ max of BTB was observed to be greater than that of BCG in all of the nonionic micellar systems investigated in buffered medium. The observed red shift has been attributed to stabilization of the base form of the dye by the polyoxyethylene (POE) head groups. The stabilization effect was found to decrease with increase in the number of carbon atom and unsaturation in the hydrophobic tail of the surfactant molecules. The Equilibrium constant of the Partition of the dyes between micellar and aqueous pseudophases (K ass ) was found to be greater for the more hydrophobic BTB than the less hydrophobic BCG. With the surfactants the K ass increases in the order Tween 80 < Tween 60 < Tween 40 < Tween 20 < TX 100. The pK a2 of the dyes were predicted using a Partition Equilibrium model and found to be in good agreement with the experimental values.

  • A Partition Equilibrium study of sulfonephthalein dyes in anionic surfactant systems: determination of CMC in buffered medium
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
    Co-Authors: Palash M. Saikia, Surashree Sarma, Biren Gohain, Achyut Kalita, Robin K. Dutta
    Abstract:

    Abstract A spectrophotometric method has been reported which can be used to simultaneously determine Partition Equilibrium constant of anionic sulfonephthalein (acid–base indicator) dyes between micellar pseudophase and aqueous phase, and critical micelle concentration (CMC) of the surfactants in buffered aqueous anionic surfactant systems. The method is based on two assumptions: (1) only one form of the dye goes into the micellar pseudophase, which holds for similarly charged dye–surfactant systems and (2) the activity terms for the conjugate acid and base forms of the dye can be combined in buffered solution. An absorption band, which decreases with addition of surfactant, is used for the analysis. The method has been found suitable to the systems of sulphonephthalein (anionic) dyes, viz. bromophenol blue (BPB), bromothymol blue (BTB) and thymol blue (TB) with anionic surfactants, viz. sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfonate (SDSN). The Partition Equilibrium constants have been found to be dependent on hydrophobicity of the dye and pH of the solutions. The CMC's have been found to increase with increase in pH for a particular buffer system. The method can conveniently be used for study of interactions in such dye–surfactant systems and to determine CMC of the anionic surfactants in buffered solutions.

Ana Coutinho - One of the best experts on this subject based on the ideXlab platform.

  • Oligomer Stoichiometry of Membrane-Bound Proteins Involved in a Cooperative Partition Equilibrium: A Homo-FRET Study
    Biophysical Journal, 2015
    Co-Authors: Ana M. Melo, Alexandre Fedorov, Manuel Prieto, Ana Coutinho
    Abstract:

    An analytical framework that uses energy homo transfer to directly probe quantitatively the oligomerization state of membrane-bound proteins engaged in a three-state cooperative Partition is presented [1]. It was assumed that monomeric proteins Partition into the bilayer surface and reversibly assemble into oligomers with k subunits [2]. A general equation relating the overall steady-state fluorescence anisotropy of the sample to its fractional labeling was derived by considering explicitly that the anisotropy of mixed oligomers containing i-labeled monomers is inversely proportional to the number of labeled subunits per oligomer (Runnels and Scarlata limit). This method was very robust in describing the electrostatic interaction of Alexa 488 fluorescently-labeled lysozyme (Lz-A488) with phosphatidylserine-containing membranes. The pronounced decrease detected in the fluorescence anisotropy of Lz-A488 always correlated with the system reaching a high membrane surface density of the protein (low L/P molar ratio). The occurrence of energy homo transfer-induced fluorescence depolarization was further confirmed by measuring the anisotropy decays of Lz-A488 under these conditions. A global analysis of the steady-state anisotropy data obtained under a wide range of experimental conditions (variable anionic lipid content of the liposomes, L/P molar ratios and protein fractional labeling) confirmed that membrane-bound Lz-A488 assembled into oligomeric complexes, possibly with a stoichiometry of k= 6 ± 1. This study illustrates that even in the presence of a coupled Partition/oligomerization equilibria, steady-state anisotropy measurements can be used to monitor the self-assembly of membrane-bound proteins.References[1] Melo et al. 2014 Phys.Chem.Chem.Phys 16: 18105[2] Melo et al. 2013 J.Phys.Chem. B 117: 2906Support from FCT/Portugal is acknowledged (projects PTDC/BBB-BQB/2661/2012 and RECI/CTM-POL/0342/2012). A.M. Melo current address is Dept Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut, US.

  • Exploring homo-FRET to quantify the oligomer stoichiometry of membrane-bound proteins involved in a cooperative Partition Equilibrium
    Physical chemistry chemical physics : PCCP, 2014
    Co-Authors: Ana M. Melo, Manuel Prieto, Aleksander Fedorov, Ana Coutinho
    Abstract:

    The establishment of protein–protein interactions between membrane-bound proteins is associated with several biological functions and dysfunctions. Here, an analytical framework that uses energy homo transfer to directly probe quantitatively the oligomerization state of membrane-bound proteins engaged in a three-state cooperative Partition is presented. Briefly, this model assumes that monomeric protein molecules Partition into the bilayer surface and reversibly assemble into oligomers with k subunits. A general equation relating the overall steady-state fluorescence anisotropy of the sample to its fractional labeling was derived by considering explicitly that the anisotropy of mixed oligomers containing i-labeled monomers is inversely proportional to the number of labeled subunits per oligomer (Runnels and Scarlata limit). This method was very robust in describing the electrostatic interaction of Alexa Fluor 488 fluorescently labeled lysozyme (Lz-A488) with phosphatidylserine-containing membranes. The pronounced decrease detected in the fluorescence anisotropy of Lz-A488 always correlated with the system reaching a high membrane surface density of the protein (at a low lipid-to-protein (L/P) molar ratio). The occurrence of energy homo transfer-induced fluorescence depolarization was further confirmed by measuring the anisotropy decays of Lz-A488 under these conditions. A global analysis of the steady-state anisotropy data obtained under a wide range of experimental conditions (variable anionic lipid content of the liposomes, L/P molar ratios and protein fractional labeling) confirmed that membrane-bound Lz-A488 assembled into oligomeric complexes, possibly with a stoichiometry of k = 6 ± 1. This study illustrates that even in the presence of a coupled Partition–oligomerization Equilibrium, steady-state anisotropy measurements provide a simple and reliable tool to monitor the self-assembly of membrane-bound proteins.